Purpose. Given a rod → rod-bipolar (RB) convergence in mammalian retina of 20-60 (1), and the ability of a RB to convey single-photon responses from any of its rod inputs, the RB is a sensitive amplifier of low amplitude rod responses. Since recent work supports identification of the rod-driven ERG b-wave with an RB field potential, we used the mouse rod b-wave as an indicator of completeness of recovery of the rod circulating current after conditioning flashes (CFs) eliciting 200-10,000 photoisomerizations/rod (Φ). Methods. 2-6 month old CBA/CAJ mice were dark adapted, anesthesized by i/p injection of a ketamine/xylazine/ urethane blend and their full-field corneal ERG recorded as described previously (2). Probe flashes (PFs) producing 45,000 Φ were used to monitor a-wave recovery, while PFs producing only 0.3 Φ and delivered at 0.5 s intervals were used to monitor b-wave recovery. Results. CFs producing 200-3000 Φ completely suppressed the a-wave for 0.2-1 s, and the rod b-wave for 1-5 s. The a-wave amplitude recovered with an isomorphic shape that translated on the time axis by 0.2 s per e-fold increase in Φ. In contrast, the b-wave recovered much more slowly, translating 2.0 s per e-fold increase in Φ. Control experiments showed rod b-wave recovery after offset of b-wave-saturating steady backgrounds (∼100 Φ/s) to be quite rapid, being complete in < 2 s. Conclusions. Slow recovery of the rod b-wave generator (RB) per se does not appear to be the cause of the slow recovery after CFs of 200-3000 Φ. Rather, the results suggest that a small amplitude, persistent signal from all the rods converging on an RB may be the cause of the slow b-wave recovery, and that the b-wave provides a useful tool for characterizing this slow rod-generated "tail" signal.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Feb 15 1996|
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